1. Field of the Invention
The present invention relates to a monitoring system, in particular to a monitoring system applied for monitoring a bridge structural safety.
2. Description of the Related Art
As bridge inspection is a continuous ongoing job, and the inspection is divided into the following two types according to its purpose:
1. A timely inspection for monitoring a situation such as a water level or an exposure extent of a bridge pier timely provides the current situation prior to the occurrence of a disaster or an emergency situation.
2. A periodical inspection for testing factors such as deformation, displacement, force distribution, appearance damage or material deterioration that may affect or change a bridge system.
At present, the bridge inspection methods adopted by Taiwan, R.O.C. for daily inspections are divided into the following three kinds in accordance with the Maintenance Manual for Railways and Bridges promulgated by the Ministry of Transportation and Communications:
(a) Regular Patrol: it takes place weekly or daily;
(b) Periodic Inspection: it takes place twice a year; and
(c) Special Inspection: it takes place after the occurrence of a disaster or an emergency situation.
Three main inspection methods are visual inspection, non-destructive inspection and destructive inspection.
The inspection procedure includes a visual observation of a bridge, and a non-destructive or a destructive inspection of the bridge whenever there is any doubt, wherein the non-destructive inspection includes the following:
(1) Surface hardness method;
(2) Surface strength method;
(3) Acoustic wave inspection method;
(4) Maturity inspection method; and
(5) Comprehensive inspection method.
The destructive inspection exerts a pressure or a pulling force at a portion of the structure to create a destructive effect to test a structural strength.
In the conventional method, the visual inspection is the most important step of the bridge inspection, and standards of evaluating a bridge condition include DER&U evaluation and ABCDN evaluation methods, for example.
DER&U evaluation method is a visual inspection and evaluation method for bridges jointly developed by Join Engineering Consultants, and South African CSIR Company, and the bridge inspection is divided into 21 inspection items, wherein the first to eleventh items relate to general inspections and overall macro inspections of bridges, and the twelfth to twentieth items relates to span inspection, and the twenty-first item relates to miscellaneous inspections.
ABCDN evaluation method is a visual inspection and evaluation method for bridges developed by China Engineering Consultants in 1996 for Taiwan Provincial Government and Department of Urban Development. The ABCDN evaluation method divides a bridge structure into eight main structures, respectively: bridge deck components, upper structure, bridge pier, foundation and soil, bridge abutment and approach, support, variable gap and other accessory facilities, and each type of structures is divided into several inspection objects, and each inspection object is subdivided into several inspection items, and all inspection items are categorized into four grades (A˜D), and an inspection item is categorized as Grade N if such inspection item is not applicable or its damage condition cannot be determined
TABLE 1DER&U Evaluation Guideline01234LevelN/AGoodAveragePoorSeriouslyDamagedScopeUninspectableImportanceUndeterminableTinyLowMiddleHighUrgencyUndeterminableRoutineWithin 3Within 1EmergencyMaintenanceyearsyearHandling andMaintenance
TABLE 2ABCDN Evaluation GuidelineGradeConditionsASlight damage requires key-point inspection.BSome damages require further monitoring, and repairs if needed.CSignificant damages require repairs. Deformation keepsoccurring, and the functionality may drop.DSignificant damages with substantial deformation and dropof functions of the structure require emergency repairsto assure the safety and smoothnessof traffic or avoid hindering a third party.NNot applicable, or the damage condition is undeterminable.OKOccasions other than those mentioned above.
The periodical inspection of a bridge adopts a visual inspection of the characteristics, and uses each standard to determine the conditions of the bridge. Even for an automated process, the process is connected automatically to a database used by the DER&U or ABCDN as a determination basis to facilitate an engineer at site to determine the bridge conditions.
In addition, most automatic monitoring technologies used for monitoring a displacement and a deformation of a bridge are measured by a contact method, and sensors are installed at different places on the bridge, such as displacement sensors are installed for measuring displacement pointwise, strain sensors are buried for measuring the strain level of bridge's structures, and acceleration sensors are used for measuring the vibration of the bridge. The aforementioned sensors are provided for converting measured physical parameters, such as deformation, stress, strain and acceleration into signals to establish a bridge deformation measuring system.
As to the measurement of water depth of a river, vertical resistors are preinstalled onto a bridge pier, and the change of resistance caused by a water level can be used for measuring the water depth of the river, and the extent of exposure of the bridge pier.
The bridges in the U.S. are inspected by the Federal Highway Administration (FHWA), and the inspections are categorized into the following five types:
(1) Routine examination (2 or 4 years);
(2) Key damage examination;
(3) Special characteristic examination;
(4) Underwater inspection; and
(5) Other inspections.
The aforementioned routine examination is equivalent to the periodical inspection of the Ministry of Transportation and Communications of R.O.C., wherein the visual inspection is adopted or photos are taken during a normal inspection period not exceeding 24 months. In addition to taking photos of a damage or a deterioration of the bridge, cross-sectional drawings and data of a river, component examination forms, work suggestions, component identifications are key damage characteristics required to be stored into the database, and a change of time of the database is used for determining whether or not to perform a destructive inspection. The database includes SMART, BIRIS and bridge references, and other items include key damage examination, special characteristic examination, underwater examination, and other examinations are categorized as special inspection.
From the description above, the U.S. bridge examination methods are the same as the R.O.C. inspection methods, and both are based on the manually measured records and neither is a bridge structural safety monitoring system with a visual observation function.
In the aforementioned methods, bridges are examined passively according to the laws and regulations, and none of the methods can provide a structural damage report timely/anytime or provide an early warning or in-time warning. In an extreme weather condition (such as a typhoon or a heavy storm) or after an earthquake occurs, the bridge may be damaged seriously and cannot be inspected visually timely. Related engineers or technicians are sent to the dangerous sites for the inspection. Particularly, in the extreme weather condition, the engineers and technicians are unable to reach the site to inspect the bridge or provide an early warning when the bridge could be seriously damaged, and it may result in an injury of the citizen and the property loss.